First it was rolled up sheets of carbon atoms known as carbon nanotubes, and then stable, two-dimensional sheets of carbon known as graphene. Now, researchers have rolled graphene back up into structures called carbon 'nanoscrolls', which have properties similar to both nanotubes and graphene — including high mechanical strength and high current transport — as well as some unique properties of their own.

Fig. 1: Carbon nanotubes (left) consisting of one or several concentric rolls of single-atom carbon sheets, and carbon nanoscrolls (right) consisting of one carbon sheet rolled up into a spiral.

Nanoscrolls, as the name suggests, are made by rolling up graphene sheets (Fig. 1), and although there are various methods for synthesizing these structures, existing approaches tend to yield only a few nanoscrolls of poor quality. Researchers at Tsinghua University in Beijing, China,1 have now optimized a simple technique for producing nanoscrolls integrated into a semiconductor device structure.

“We think the carbon nanoscrolls may be suited for many applications,” says Li Qunqing, a member of the team. “For example, they may be useful for making interconnects in microcircuits or hydrogen storage.”

To make the nanoscrolls, the group started by rubbing bulk graphite to afford graphene flakes. The flakes were rubbed off onto an oxidized silicon substrate, to which the graphene adhered naturally. The researchers then applied a drop of isopropyl alcohol to each flake, which caused the exposed layer of the graphene flake to become strained, thereby inducing the flake to roll up like a scroll.

Qunqing's team is one of the first to be able to test the potential of the nanoscrolls for electronic device applications. They found that the nanoscrolls were relatively free of charge impurities, and because they were made from a single sheet of graphene — rather than concentric rolls as in nanotubes — current flowed through the entire structure.

This means that the nanoscrolls can support high current densities, an attractive feature for making interconnects in microcircuits. Moreover, the nanoscrolls may also be useful in hydrogen storage by rolling up graphene sheets bearing adsorbed hydrogen; conventional approaches have hydrogen being 'pushed' into carbon nanotubes.